Deformation Characteristics, Kinematic Analysis, and Formation Ages of Mylonites in the Ductile Shear Zone

A special issue of Minerals (ISSN 2075-163X).

Deadline for manuscript submissions: closed (31 December 2023) | Viewed by 2720

Special Issue Editors


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Guest Editor
College of Earth Sciences, Jilin University, Jianshe Street 2199, Changchun 13006, China
Interests: structural geology; tectonics; geochronology
School of Resources and Environmental Engineering, Shandong University of Technology, Xincunxi Road 266, Zibo 255000, China
Interests: structural geology; tectonics
College of Earth Sciences, Jilin University, Jianshe Street 2199, Changchun 130061, China
Interests: structural geology; rheology; tectonics

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Guest Editor
Key Lab of Submarine Geosciences and Prospecting Techniques, MOE and College of Marine Geosciences, Ocean University of China, Qingdao 266100, China
Interests: tectonics; geochronology; geochemistry

Special Issue Information

Dear Colleagues,

As we know, ductile shear zones are narrow, planar, and where the strain is locally concentrated relative to their surrounding regions, and their structural styles have important implications for the regional tectonic evolution worldwide. Structural geologists have long been interested in ductile shear zones. Most of these ductile structures are characterized by mylonite or high-strain (straight) gneiss which are the products of ductile deformation in the middle to lower crust, with elongation lineations, dynamic recrystallization, augen structures, and S-C fabrics that strongly and necessarily have causal relationships with deformation, temperatures, shear strain, rheological parameters, and various meso- and micro-structures. The shear sense, formation ages, composition of the rocks deformed, kinematic characteristics, and evolutionary history remain to be confirmed by detailed meso- and macro investigations.

This Special Issue aims to contribute to the existing knowledge of the links between ductile shear zones and different types of gneiss or mylonite, and to decipher their fabric evolution or tectonic evolution which is related to strain intensities, shear type, the dynamic recrystallization process, as well as meso- and micro-structures.

Dr. Chenyue Liang
Dr. Chao Zhang
Dr. Weimin Li
Dr. Qingbin Guan
Guest Editors

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Keywords

  • mylonite
  • kinematic vorticity
  • ductile shear zone
  • EBSD analysis
  • deformation temperature
  • deformation mechanism
  • formation age
  • tectonic evolution

Published Papers (2 papers)

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Research

28 pages, 29060 KiB  
Article
Metamorphism and P-T Evolution of High-Pressure Granulites from the Fuping Complex, North China Craton
by Zijing Zhang, Changqing Zheng, Chenyue Liang, M. Santosh, Junjie Hao, Lishuai Dong, Jianjun Hou, Feifei Hou and Meihui Li
Minerals 2024, 14(2), 138; https://doi.org/10.3390/min14020138 - 26 Jan 2024
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Abstract
Granulite facies rocks provide important keys to evaluating collisional metamorphism in orogenic belts. The mafic granulites of Baoding in the Fuping Complex of the North China Craton occur within the Trans-North China Orogen (TNCO), a major Paleoproterozoic collisional orogen. Here, we present results [...] Read more.
Granulite facies rocks provide important keys to evaluating collisional metamorphism in orogenic belts. The mafic granulites of Baoding in the Fuping Complex of the North China Craton occur within the Trans-North China Orogen (TNCO), a major Paleoproterozoic collisional orogen. Here, we present results from detailed investigations on newly discovered garnet pyroxenite, garnet two-pyroxene granulite, and garnet-bearing-plagioclase amphibolite using petrographic, mineralogical, geochemical, and zircon U-Pb dating methods. Our results show that the Fuping Complex metamorphic evolution in this study evolved in four stages: prograde (M1), high-pressure granulite facies (M2), granulite facies (M3), and retrograde (M4) stages. The mineral assemblage of the prograde stage (M1) consists of Amp + Pl + Q within garnet cores. The mineral assemblage of high-pressure granulite facies at the peak stage (M2) consists of Gt + Cpx + Pl + Q ± Amp, forming the garnet pyroxenite. The granulite facies stage M3 is characterized by the occurrence of orthopyroxene, with a mineral assemblage of Gt + Cpx + Opx + Amp+ Pl + Q. The early retrograde stage M4-1 includes clinopyroxenes scattered inside amphiboles, following the breakdown of garnet and clinopyroxene. The mineral assemblage of this stage comprises Amp + Pl + Q + Ilm ± Cpx. Later, in the late retrograde stage M4-2, the composition of amphiboles changed to actinolite, and epidote and chlorite started to appear in the matrix. Traditional geothermobarometry yielded P-T conditions of 700~706 °C and 6.0~6.2 kbar for prograde stage M1, 854~920 °C and 13.0~13.8 kbar for high-pressure granulite facies stage M2, 912~939 °C and 8.1~9.9 kbar for M3, 661~784 °C and 3.1~4.4 kbar for M4-1, and 637~638 °C, 1.1~1.3 kbar for M4-2, along a clockwise P-T path with a nearly isothermal decompression (ITD) and slight heating. Zircon LA-ICP-MS U-Pb dating constrains the timing of the high-pressure granulite facies metamorphic event to be between 1.83 and 1.86 Ga. Geochemical features suggest that the protoliths of the high-pressure granulites may have formed in an island arc environment within a convergent margin setting. Together with results from previous studies, our data suggest that the ~1.85 Ga metamorphic age recorded in the Fuping Complex represents a regional metamorphism in the TNCO, associated with the subduction–collision and assembly of the Eastern and Western Blocks of the NCC. Full article
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18 pages, 14651 KiB  
Article
Microstructural Relationship between Olivine and Clinopyroxene in Ultramafic Rocks from the Red Hills Massif, Dun Mountain Ophiolite
by Yilun Shao, Marianne Negrini, Cai Liu and Rui Gao
Minerals 2023, 13(11), 1415; https://doi.org/10.3390/min13111415 - 6 Nov 2023
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Abstract
The microstructural relationship between olivine and clinopyroxene is significant in recovering the mantle evolution under clinopyroxene-saturated melting conditions. This study focuses on olivine/clinopyroxene-related ultramafic rocks (dunite, wehrlite, olivine clinopyroxenite, and clinopyroxenite) in the Ells Stream Complex of the Red Hills Massif. (Olivine) clinopyroxenites [...] Read more.
The microstructural relationship between olivine and clinopyroxene is significant in recovering the mantle evolution under clinopyroxene-saturated melting conditions. This study focuses on olivine/clinopyroxene-related ultramafic rocks (dunite, wehrlite, olivine clinopyroxenite, and clinopyroxenite) in the Ells Stream Complex of the Red Hills Massif. (Olivine) clinopyroxenites have an A/D-type olivine crystallographic preferred orientation (CPO) whereas peridotites have various olivine CPO types. B-type olivine CPO was newly discovered, which may have been generated under hydrous conditions. The discovery of B-type CPO means that all six olivine CPO types could exist in a single research area. Clinopyroxene CPOs also vary and have weaker deformation characteristics (e.g., lower M index and weaker intracrystalline deformation) than olivine; thus, they probably melted and the clinopyroxene-rich ultramafic bands existed as melt veins. Irregular clinopyroxene shapes in the peridotites and incoherent olivine and clinopyroxene CPOs ([100]OL and [001]CPX are not parallel) also indicate a melted state. The dominant orthorhombic and LS-type CPOs in olivine and clinopyroxene imply that simple shear was the main deformation mechanism. Such complicated microstructural characteristics result from the overprinted simple shear under high temperatures (>1000 °C) and hydrous melting environments until the melt-frozen period. This case study is helpful to better understand the olivine and clinopyroxene relationship. Full article
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